Location specificity in perceptual learning can be eliminated through proper training procedures (Xiao et al., CurBio_08), suggesting that learning may result from training improved decision making in non-retinotopic high brain areas. This conclusion gains support from ERP recordings in this study. We trained observers with a Vernier task in the lower right visual field for six days. Pre- and post-training thresholds were compared at the trained and untrained (lower left visual field) locations. 64-channel EEG was recorded pre-/post-training at the trained and untrained locations for Vernier offsets either near the pre-training threshold (5′) or sub-threshold (2.8′). Our results show that (1) Vernier learning was specific to the trained location in most observers but transferred significantly in the remaining observers. (2) The frontal P2 (210∼270ms), which may be related to decision making, had shorter latency and smaller amplitude after training for all observers showing or not showing location specificity at both locations. (3) The posterior N1 (160ms-200ms), which may be related to spatial attention, increased significantly after training at the trained location but decreased at the untrained location in observers showing location specificity. However, posterior N1 increased significantly at both trained and untrained locations for observers who showed significant learning transfer. (4) The EEG differences were similar at Vernier offsets either near pre-training threshold, which became supra-threshold post-training, or sub-threshold, which became near-threshold post-training. The ERP evidence is consistent with our rule-learning based perceptual learning model, in which a decision unit in the high-level brain learns the rules of reweighing the V1 inputs (better decision making). Such reweighing rules are unspecific to stimulus locations. However, learned rules can only apply to a new location if the brain can attend to the V1 inputs at the new location properly. The latter can be accomplished through location training.